GCSE Biology Unit 2 (4)

Osmosis

• Osmosis is just a special case of diffusion
• Osmosis is the movement of water molecules across a partially permeable membrane from a region of high water concentration to an area of low water concentration.
• A partially permeable membrane is one with very small holes in it. 
• So small that only tiny molecules such as water can pass through them, and bigger molecules (e.g. glucose) can't.
• The water molecules actually pass both ways through the membrane during osmosis.
• This happens because water molecules move about randomly all the time.
• But because there are water molecules on one side than the other, there's a steady net flow into the region with fewer water molecules.
• The water acts like it's trying to even up the concentration on either side of…